Fluid cooled electrosurgical cauterization system

ABSTRACT

An electrosurgical probe is disclosed which provides the ability to both cut and cauterize tissue. The probe includes at least one cauterization electrode mounted upon a distal portion of the electrode and adapted to deliver electrosurgical energy to tissue. Further, a central lumen is disposed within the probe. The lumen is adapted to accommodate the flow of fluid from a remote source to tissue through an outlet port in the distal end of the probe. Also, the lumen houses a cutting electrode which is selectively deployable. Both cauterization and coagulation can be conducted in a bipolar mode. The flow of fluid through the lumen serves to limit the heat transfer from the cauterization electrode to adjacent tissue to an extent sufficient to prevent the sticking of tissue to the probe. A feedback system is also provided to optimize the electrode temperature.

This is a continuation of application Ser. No. 07/975,801 filed on Nov.13, 1992, now U.S. Pat No. 5,342,357.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery.More particularly, the present invention relates to a system forcontrolling heat transfer from surgical electrodes to adjacent tissue.

During the course of surgical procedures it is often necessary tocauterize or coagulate tissue to control bleeding. Electrosurgicaldevices are known which utilize electrical current for tissuecauterization. U.S. Pat. Nos. 1,983,669 and 4,637,392 discloseelectrical cauterization devices in which electrodes are disposed aboutthe surface of a probe. Tissue is heated and coagulation is effected bydelivering electrosurgical energy to tissue through the electrodes.Among the drawbacks of such devices is the potential that the electrodeswill become overly heated, thus prematurely dessicating the tissue andcausing the tissue to stick to the electrodes. This can result infurther bleeding upon disengagement of the electrodes from the tissue,and the need to remove tissue from the electrode before continuing touse the device. Moreover, it can be inconvenient to use suchcauterization devices during certain surgical procedures because cuttingand cauterization must be performed with separate instruments.

Various electrosurgical probes exist for transferring energy to abiological site. Typically these probes dispose a metallic electrodealong the outer surface of a rigid shaft. When the probe is positionedwithin the patient, the probe is in contact with the tissue at thesurgical site. As energy is transferred through the electrode,electrical currents are established within adjacent tissue. As currentpasses through the tissue, some energy is absorbed into the tissuecausing tissue temperature to rise. The rising temperature of the tissuedenatures tissue protein molecules and facilitates coagulation.

Among the drawbacks of such devices is the potential that the electrodeswill become overheated, and the denatured proteins will weld to theelectrode on the outer surface of the probe. This can result in tissuesearing or dessication, or in tissue being torn from the surgical siteas the probe is removed from the patient. Such a tear can result inbleeding or the reopening of a wound. A further problem results fromtissue collecting over the probe. Tissue stuck to the probe interfereswith the delivery of energy to the surgical site. This interferencelimits the depth of penetration of energy into the tissue and therebylimits the depth of cauterization. Because of these drawbacks thesedevices are impractical for certain surgical procedures.

Surgical systems exist that attempt to limit the sticking of tissue tosurgical probes. Some thermal cauterizing probes have placed a non-stickcoating of teflon® around the thermal electrode. However, because teflondoes not conduct electricity the use of this technique forelectrosurgical probes is impractical. Some electrosurgical systemsmonitor the temperature of the electrodes at the probe and reduce theenergy being transferred to the site in order to control the temperatureof the probe. This process results in a fluctuating energy density beingdelivered to the surgical site and a resulting uncertainty as to thedepth of cauterization being effected.

There is a need for an electrosurgical device and system that canperform tissue cutting procedures and tissue cauterization procedureswithout overheating and causing tissue to stick or weld to theelectrode. Such a device would be useful in that it would eliminate theneed for the surgeon to scrape tissue and/or coagulant from the probeduring the cauterization or cutting procedure. A device of this typewould be well suited to general surgical procedures as well as tomicrosurgical procedures.

Accordingly, it is an object of the present invention to provide asurgical device and system that controls the transfer of heat from thedevice to tissue at the surgical site. A further object of the inventionis to provide such a device that is adapted to control the temperatureof an electrode mounted on an electrosurgical device. Yet another objectof the invention is to provide an electrosurgical device that controlsthe transfer of heat from the electrode to adjacent tissue withoutlimiting the electromagnetic energy delivered to the tissue. It is alsoan object of the invention to provide an electrosurgical device thatprevents tissue and/or coagulant from welding to an energy deliveringelectrode. Other objects of the invention will be apparent upon readingthe description which follows.

SUMMARY OF THE INVENTION

In one embodiment the present invention comprises an electrosurgicaldevice that includes an elongate surgical probe member having disposedabout a portion of its outer surface dual cauterization electrodes thatare electrically isolated from each other. In one embodiment thecauterization electrodes may be helically oriented about the outersurface of the probe member. A longitudinally oriented lumen extendsthrough the member and is adapted to deliver a fluid through the memberfrom a fluid source. The lumen has at least one outlet port, preferablyat the distal end of the member, through which the fluid can bedischarged. The device also includes a selectively deployable cuttingelectrode that is able to be retracted within the lumen when not in use,and to be extended from the lumen upon deployment. The fluid deliveredthrough the lumen serves both to cool the cauterization electrodesduring cauterization, and to irrigate the surgical site.

The device is used in conjunction with an electrosurgical generator thatsupplies electrosurgical energy to the cauterization electrodes and tothe cutting electrode. Switches are provided to enable a surgeon toswitch easily between the cutting and coagulation modes, and toselectively deliver fluid through the lumen at desired flow rates.

When used for cauterization the device can function in a bipolar modewith the dual cauterization electrodes being electrically isolated fromeach other. The device also may be used as a bipolar surgical device forperforming cutting procedures with the cutting electrode serving to cuttissue, and one or both of the cauterization electrodes serving asreturn electrodes.

In another embodiment the device serves only as a cauterization probeand does not include a cutting electrode.

A control system associated with the device facilitates the controltemperature of the energy delivering electrode (especially in thecauterization mode) to prevent excess heating of the electrode and/orthe delivery to the electrode of excess energy. In one embodiment thetemperature of the energy delivering electrodes is monitored andcompared to a predetermined maximum temperature value. The flow rate offluid delivered through the lumen is controlled, based upon the comparedtemperature values, to maintain electrode temperature at or below thepredetermined value. Flow rate can be increased if the measuredtemperature exceeds the predetermined value. Similarly, flow rate can bemaintained or decreased if the measured temperature equals or is belowthe predetermined value.

The energy output by the generator to the probe may also be controlledbased on measured tissue impedance, in conjunction with the monitoringof electrode temperature. Upon delivery of energy to tissue, theimpedance value is then compared to a predetermined maximum impedancevalue. If the measured impedance exceeds the predetermined impedancevalue, a signal is generated and transmitted to the generator to preventfurther delivery of energy by the generator. This system serves as anadded safety measure to prevent injury to a patient as a result ofdelivering too much energy through the probe or excessively heatingtissue. The measured tissue impedance value may also be used to controlthe fluid flow rate, independent of temperature monitoring.

The device is useful for general surgical applications in which thecutting and cauterization probe directly accesses a target site througha percutaneous incision located proximal to the target site. Inaddition, the probe may be manufactured in dimensions suitable for usein microsurgical procedures where the probe can be delivered to thetarget during arthroscopic, endoscopic, or laproscopic surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an electrosurgical cutting and coagulationsystem constructed according to the present invention.

FIG. 2 is a perspective view of an electrosurgical probe useful with thesystem illustrated in FIG. 1.

FIG. 3A is a perspective view of a forward portion of theelectrosurgical probe illustrated in FIG. 2.

FIG. 3B is a front end view of the probe illustrated in FIG. 3A.

FIG. 3C is a perspective view of the probe illustrated in FIG. 3A, withthe cutting electrode in the retracted position.

FIG. 4 is a side view partially cut away, of a rear portion of theelectrosurgical probe of FIG. 2, illustrating a knob for controlling theextension and retraction of the cutting electrode.

FIG. 5 is a side view, partially cut away, illustrating a portion of theelectrosurgical probe of FIG. 2 constructed according to the presentinvention.

FIG. 6 is a sectional view along lines 6--6 of the probe illustrated inFIG. 3A.

FIG. 7 is an alternative embodiment of the electrosurgical probeillustrated in FIG. 3A, having a side-mounted fluid outlet port.

FIG. 8 is schematic view of an electrosurgical cauterization systemaccording to the present invention.

FIG. 9 is a perspective view of a forward portion of an electrosurgicalcauterization probe useful with the system of FIG. 8.

FIG. 10 is a sectional view, allow lines 10--10 of the electrosurgicalcauterization probe of FIG. 8.

FIG. 11 is a block diagram illustrating the temperature and impedancefeedback control system of the invention.

FIG. 12 illustrates a circuit useful in implementing the temperature andimpedance feedback control system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the electrosurgical cutting and coagulation system 10of the present invention. The system 10 comprises a radio frequencyenergy source 12, a control unit 14, in electrical communication withthe energy source, and an electrosurgical probe 16. The control unit 14is in electrical communication with probe 16 through electrode leads 18,20, 22. Further, a fluid source 24 communicates a fluid to probe 16through conduit 26.

The electrosurgical cutting and cauterization probe 16 is furtherillustrated in FIGS. 2 through 3C. As illustrated, probe 16 has a handleportion 28 at its proximal end and an elongate member 30 that extendsfrom the handle portion. The distal end of elongate member 30 issomewhat tapered and includes a cauterization tip 32 and a retractablecutting electrode 34. Cutting electrode 34 is able to extend from, or tobe retracted within, a substantially circular orifice 36 whichpreferably is disposed in the distal end of cauterization tip 32. Theexposed outer surface 33 of the cauterization tip 32 includes dualcauterization electrodes 38, 40. Preferably, cauterization electrodes38, 40 are helically oriented about the surface 33 of cauterization tip32. However, other orientations for electrodes 38, 40 are possible aswell.

The handle portion 28 of probe 16 includes a fluid inlet port 42 thatcommunicates with fluid source 24 through conduit 26. Electrode leads 20and 22 emerge from a cuff 44 on the handle portion 28 of the probe. Theproximal ends of leads 20, 22 have connectors 46, 48, which are matablewith control unit 14. The distal ends of leads 20 and 22 connect tocauterization electrodes 38 and 40, respectively.

Cutting electrode 34 extends throughout the length of probe 16, andpreferably has a length greater than the probe itself so that it is ableto emerge both from the distal end of member 30 and the proximal end ofhandle 28. An electrode lead 18, having connector 50, connects theproximal end 34A of cutting electrode 34 to control unit 14. Cuttingelectrode 34 preferably is coated with an insulating material over itsentire length, except for its extreme distal end which is uncoated so asto deliver electrosurgical energy to tissue. Suitable insulatingmaterials include polymers such as polyvinylidene fluoride,polytetrafluoroethylene, fluorinated ethylene-propylene polymers,polyethylene, and others known to be suitable for use in medicalapplications.

Referring to FIGS. 4, 5, and 6, lumen 52 preferably is centrally locatedwithin probe 16 and extends throughout the length of the handle portion28 and elongate member 30, along the longitudinal axis of the probe. Theinlet port 42 provides a passageway for fluid to be communicated fromconduit 26 to lumen 52. A fluid from source 24 is thus able to becommunicated to inlet port 42 to enable fluid to be delivered throughthe lumen to the orifice 36 where it is discharged from the probe tocontact tissue.

In an alternative embodiment, illustrated in FIG. 7, a side-mountedorifice 60, in fluid communication with lumen 52, may be used todischarge fluid to adjacent tissue. Orifice 60 may be used alone, or incombination with orifice 36. Also, orifice 60 may, if desired, be pairedwith one or more additional side-mounted orifices (not shown).

As noted, cutting electrode 34 is positioned within and extends over theentire length of lumen 52. The selectively deployable nature of cuttingelectrode 34 is advantageous in that electrode 34 can be deployed for acutting procedure and retracted during cauterization.

Deployment of electrode 34 can be controlled by a suitable mechanismpreferably mounted on the handle portion 28 of probe 16. FIG. 4illustrates a thumbscrew 54, mounted upon the proximal end of handle 28,which can be used to control the retraction and extension of the cuttingelectrode 34. Alternatively, as shown in FIG. 1, an excess length ofelectrode 34 may extend from the proximal end of handle 28 so as to bemanually manipulated to regulate the length of electrode 34 extendingfrom orifice 36. A variety of other length controlling mechanisms may beutilized as well.

In one embodiment cutting electrode 34 may be biased either to anextended or retracted position. The biasing force may be overcome by themechanism used to control the extension/retraction of electrode 34.

The dimensions of the probe 16 are such that it is suitable for use inarthroscopic, endoscopic, laproscopic, and general surgery. Preferably,the length of the probe is approximately 10 to 18 inches. The diameterof member 30 can vary within a range of dimensions known in the art tobe suitable for the intended use of the probe. In a preferredembodiment, the diameter is not constant along the entire length ofmember 30. Member 30 preferably has approximately three distinguishablebut integral sections which have slightly differing diameters. Asillustrated in FIG. 2, a proximal section 30A of the member 30 is thelongest segment and has the largest diameter D₁. Adjacent this sectionis portion 30B of member 30, having a slightly smaller diameter D₂. Thediameter of region 30C tapers over its entire length, terminating incauterization tip 32 which has a diameter D₃. Generally, the diameter D₁ranges from approximately 10 to 20 French (0.13 to 0.26 inch). DiameterD₂ ranges from 7 to 15 French while D.sub. 3 ranges from about 5 to 12French.

The diameter of cutting electrode 18 can also vary, and its size dependsto a large extent upon the diameter of lumen 52. One requirement of thelumen diameter is that it be sufficient to accommodate the flow of fluidwhile electrode 18 is disposed within the lumen. Generally, the lumendiameter is in the range of 3 to 7 French, while the diameter ofelectrode 34 ranges from 1 to 3 French.

The probe 16 of the present invention can be manufactured of a varietyof materials, including polyolefins and nylons, that are known to besuitable for use in medical applications. The outer wall 58 of member 30preferably is manufactured of an insulating polymeric material of thetype well known in the art and suitable for use in medical applications.

The cutting electrode 34 and cauterization electrodes 38, 40 preferablyare made from a highly conductive material such as gold, silver orplatinum. The conductive material from which the electrodes are made canbe a solid material or, alternatively, a plating which is deposited uponan insulating material such as a polymer. The cutting electrode shouldhave sufficient rigidity, tensile strength and compressive strength toenable it to be extended from and retracted within the probe 16.

As noted, the probe 16 of the present invention is useful in generalsurgical procedures as well as in laproscopic, arthroscopic, andendoscopic surgical procedures. A significant advantage of probe 16 isthat it represents a single instrument which can perform bothcauterization and cutting procedures in a bipolar mode. Moreover,cauterization with probe 16 is more effective because the fluid flowthrough lumen 52 prevents electrodes 38 and 40 from transferringexcessive thermal energy to tissue.

In operation, the probe may be inserted through an incision and directedto the location at which the surgical procedure is to be performed.Cutting electrode 34 can be extended from within lumen 52 once the probereaches the surgical site. Thereafter, electrosurgical energy can bedelivered between electrode 34 and one or both of electrodes 38, 40(serving as return electrodes) to cut tissue. Control of bleeding can beeffected utilizing cauterization tip 32 and cauterization electrodes 38and 40. To do so, tip 32 is positioned in contact with tissue requiringcauterization and electrosurgical energy is delivered between electrodes38 and 40 upon changing the mode of operation from cutting tocoagulation, using, for example, switch 56 on control unit 14. Thiscauterization procedure can be bipolar in that one of electrodes 38 and40 serves as an active, energy delivering electrode, while the otherserves as a return electrode.

FIGS. 8 through 10 illustrate an alternative embodiment of the inventionin which system 10 serves only to cauterize tissue. The probe is similarin construction to that illustrated in FIGS. 1 through 7, but it doesnot include a cutting electrode. Although lumen 52 is illustrated asbeing centrally disposed within member 30, it is understood that thelumen need not be disposed within member 30, but instead can be appendedto member 30.

During cauterization procedures, and optionally during cutting as well,fluid is delivered through lumen 52 at a desired rate. The delivery offluid serves two purposes. First, the fluid acts to limit the heattransfer from cauterization electrodes 38, 40 to adjacent tissue to anextent that tissue does not become overly heated by the electrodes,causing tissue and/or coagulant to stick to tip 32. This enables moreeffective and convenient cauterization. The fluid delivered to tissuecan also serve as an irrigant to improve the visibility in the areasubject to surgery and to remove any debris from the surgical site.

The fluid flow rate may be constant or variable. Preferably, the flowrate is variable and occurs only when energy is delivered to effectcauterization and preferably ranges from approximately 1 to 50ml/minute. One skilled in the art will readily appreciate that it may bedesirable to use a somewhat higher flow rate.

One of ordinary skill in the art will appreciate that the fluid flowrate depends on a number of variables, including the temperature of thefluid and the amount of power delivered to the cauterization electrode.The flow rate should be effective to control the temperature of thecauterization electrode, but should not be so high as to destroy tissue.The electrode temperature should be maintained below about 60° C., andmore preferably below about 46° C. The temperature of the fluid mayrange from quite cold (e.g., about 4° C.) to about room temperature orhigher (e.g., about, 27° C.).

Flow rate can be manually adjusted or can be controlled by one or morefeedback mechanisms that monitor temperature impedance and/or electrodetemperature. A suitable feedback mechanism is described below.

One skilled in the art will readily appreciate that certain surgicalprocedures will be able to tolerate more fluid flow while others will beable to tolerate less. The fluid flow rate can be adjusted toaccommodate the requirements of a variety of surgical procedures.

The fluid source 24 may communicate with a valve or pump mechanism (notshown) which controls the flow rate of fluid through lumen 52. The flowrate can be constant at a predetermined rate, such as about 30ml/minute, which generally is sufficient to limit the temperature ofelectrodes 38, 40 and cauterization tip 32.

The flow rate preferably is variable and is controlled through afeedback system that monitors electrode temperature and/or tissueimpedance. The delivery of energy through electrodes 38 and/or 40 tocauterize tissue causes the temperature of the electrodes to risesignificantly. Excess heating of the electrodes (e.g., above about 60°C.) can damage tissue and result in the buildup of excess coagulant onthe cauterization tip 32 of probe 16. Such coagulant can impede the flowof current from tip 32 to tissue and thus must be removed to enableeffective energy delivery to tissue.

The present invention utilizes a feedback system 100, illustrated inFIG. 11, that monitors electrode temperature and/or tissue impedance tocontrol the flow rate of fluid through lumen 52. The fluid passingthrough the lumen serves to cool electrodes 38, 40, and flow rate of thefluid affects electrode temperature. FIG. 11 is a block diagram thatillustrates the operation of feedback system 100. As illustrated,generator 102 delivers electrosurgical energy to probe 104 which, inturn, conveys the energy to tissue 106. Impedance of the tissue ismeasured through a circuit 108, preferably associated with thegenerator, based on the energy applied to the tissue. Circuit 108compares the measured impedance with a predetermined maximum impedancevalue. If the measured impedance exceeds the predetermined maximumimpedance a disabling signal 110 is transmitted to generator 102 tocease further delivery of energy to probe 104. Alternatively, themeasured impedance, as compared to a predetermined desired impedancevalue, can also be used to control the fluid flow rate through the probe104 to avoid excessive heating of energy delivering electrodes.

Feedback system 100 preferably monitors electrode temperaturecontemporaneous with the monitoring of tissue impedance. In a preferredembodiment the tissue impedance monitoring circuit is used to disablethe generator (if necessary) while a temperature monitoring functionfacilitates control of fluid flow rates.

As electrosurgical energy is delivered to tissue 106 from probe 104, theelectrode temperature is monitored by element 112, which may be athermistor, thermocouple, or the like. Comparator 114 compares themeasured electrode temperature value with a predetermined maximumtemperature value. Flow control element 116 regulates the fluid flowrate to achieve optimal electrode temperature based on the measuredelectrode temperature in relation to the predetermined maximumtemperature. For example, if the measured electrode temperature exceedsthe predetermined maximum temperature, flow rate will be increased.Similarly, if the measured temperature is low, flow rate will bemaintained or decreased.

Further, output 117 from the temperature comparator 114 can be input togenerator 102 to regulate the amount of power delivered by thegenerator, thus controlling temperature. Similarly, output 119 fromimpedance monitor and comparator 108 can be inputted to flow regulator116 to regulate fluid flow and thus control electrode temperature.

Although one having ordinary skill in the art will appreciate that thefeedback system of the invention can be implemented in a variety ofways, an exemplary feedback circuit is illustrated in FIG. 12.

FIG. 12 depicts an exemplary circuit to effect the system described inFIG. 11. An energy delivering means, such as RF generator 102, istransformer coupled to the probe 104, to apply a biologically safevoltage to a patient'S tissue. In this embodiment, the probe isrepresented as a bipolar cauterization probe 104 having an energydelivering electrode 38 and a ground electrode 40. Both electrodes 38,40 are connected to the primary side of the transformer windings 1, 2.The common primary winding 1, 2 is magnetically coupled via atransformer core to the secondary windings 1', 2' so that the currentand voltage of the primary side is reflected to the secondary windings1', 2'.

According to a preferred aspect of the invention, the primary windings 1of the first transformer t₁ couple the output voltage of the probe 104to the secondary windings 1'. The primary windings 2 of the secondtransformer t₂ couple the output current of the probe 104 to thesecondary windings 2'. Those of ordinary skill in the art willappreciate that the two transformers act as step-down transformers andfurther serve as means of isolating the high voltage between theelectrosurgical probe 102 and the secondary windings or measuringcircuit 1', 2'.

The measuring circuits determine the root mean square (RMS) values ormagnitudes of the current and voltage and these values, represented asvoltages, are inputted to a dividing circuit D to geometricallycalculate, by dividing the RMS voltage value by the RMS current value,the impedance of the body tissue at the probe electrode 104. Those ofordinary skill in the art will understand that the voltage presented atthe output of the divider circuit D is representative of and a functionof the impedance of the tissue adjacent to the probe electrodes 38, 40.

The output voltage of the divider circuit D is presented at thepositive(+) input terminal of comparator A. A voltage source V_(o)supplies a voltage across the variable resistor R_(v), thus allowing oneto manually adjust, via a knob, the voltage presented at the negativeinput of comparator A. This voltage represents a maximum impedance valuebeyond which power will not be applied to the probe 104. Specifically,once the tissue is heated to a temperature corresponding to an impedancevalue greater than the maximum cut-off impedance, the RF generator 102will stop supplying power to the probe 104. Comparator A can be of anycommercially available type that is able to control the amplitude orpulse width modulation of the RF generator.

In one aspect of the invention, the flow rate of the coolant can becontrolled by either the tissue impedance, as represented by signal t15,or by the probe temperature, as represented by signal 120. In onepreferred embodiment, the switch S is activated to allow the impedancesignal 115 to enter the positive(+) input terminal of comparator A. Thissignal along with the reference voltage applied to the negative(-) inputterminal actuates the comparator A to produce an Output signal. If thetissue is heated to a biologically damaging temperature, the tissueimpedance will exceed the selected impedance value seen at thenegative(-) input terminal thereby generating a signal 110 to disablethe RF generator 102, ceasing the power supplied to the probe 104.

The output signal of comparator A can further be communicated to pump125. If the temperature of the probe 104 is high, despite the tissueimpedance falling within acceptable limits, the pump 125 will adjust therate of flow of the cooling fluid subsequently applied to the probeelectrodes 38, 40 to decrease the probe temperature. Thus, the outputsignal of comparator A may either disable the RF generator's 102 poweroutput (depending on the tissue temperature as reflected by itsimpedance) or cool the probe or perform both operations simultaneously.

In another aspect of the invention, the rate of flow of the coolingfluid is controlled by the temperature measured at the catheter tip. Theswitch S is actuated so as to transfer to the positive(+) input terminalof comparator A the comparator B output signal 120. The temperaturesensor is a thermistor T, and is preferably disposed longitudinallyalong the outside body of probe 104. The thermistor T senses temperatureand reacts to differential temperature changes in a predictable manner.Thus, the thermistor actively reflects through varying resistance thetemperature it is exposed to.

Both leads of the temperature sensitive thermistor T are inputted to thepositive(+) and negative(-) terminals of comparator B to produce asignal 120 indicative of the catheter temperature. This signal 120 worksin conjunction with the reference voltage inputted at the negative(-)terminal to activate the comparator A to produce an output signal thatis electrically communicated to the pump 125. The pump 125 in responseto the signal selectively varies the flow rate of the cooling fluid asit travels through a lumen 52 disposed within the probe 104 to theenergy delivering electrode 38.

It is understood that the temperature of the electrode can becontinuously monitored or randomly sampled to ensure against excessiveheating of the tissue. Moreover, the pump employed can be a valve, orseries thereof, rather than an electrical-mechanical apparatus. Thevalve can adjust the rate of flow of the cooling liquid from the fluidsupply source in the same manner as a pump.

Virtually any generator able to provide electrosurgical energy formedical applications may be used with the present invention. Preferably,the generator 12 is a voltage determinative, low source impedancegenerator that provides radio frequency energy. A preferred generator isable to supply up to 3 amps of current and has an impedance value ofless than 10 ohms.

The energy supplied by the generator to the control unit 14 and to probe16 is preferably in the radio frequency (RF) range. Although virtuallyany frequency in the RF range may be supplied to probe 16, the preferredrange is about 500 to 700 KHz, and most preferably about 550 KHz.

As illustrated in FIG. 1, RF energy is provided to a control unit 14from a generator 12. The control unit 14 includes switching mechanism 56which enables a surgeon to control to mode of operation of the probe.Moreover, additional switches (not shown) mounted on or remote from unit14 may be used to control the delivery of energy and the magnitude ofthe delivered energy.

The energy requirements of the probe are dynamic and will vary upon theimpedance value of tissue which is being treated, and upon whether thetissue is being coagulated or cut. The impedance of tissue varies amongtissue types and the amount of blood present in or around the tissue.The amount of current delivered by the probe to tissue thus depends onthe impedance of the tissue. Where the tissue contacted has a lowerimpedance value, more current will be delivered to the tissue throughthe clip, and, conversely, less current will be delivered where thetissue has a higher impedance value. The current delivered duringcutting procedures utilizing electrode 34 generally ranges between 0.2amps and 3 amps. The voltage applied to tissue for such cuttingprocedures is between about 60 and 1000 volts rms. Current deliveredduring coagulation is generally in the range of 0.25 to 1.0 amp., andcoagulation voltages is in the range of about 10 volts to about 50 voltsrms.

It is understood that various modifications may be made to the inventiondescribed above without departing from the scope of the claims. Forexample, rather than operating in the bipolar mode, the cutting andcoagulation each may be performed in a monopolar mode with the use of aremote ground pad. Also, the mode of operation may be controlled by theuse of a foot pedal rather than a switch mounted on control unit 14.

What is claimed is:
 1. A method for controlling the temperature of anenergy delivering, cauterizing electrode, comprising:providing anelongate electrosurgical probe member having disposed at a distalportion of an outer surface thereof at least one energy deliveringcauterization electrode, the probe member having a fluid deliveringlumen associated therewith and being in electrical communication with anelectrosurgical generator unit; delivering electrosurgical energy fromthe generator unit through the probe member to the energy deliveringelectrode and adjacent tissue; measuring the tissue impedance based onthe energy applied thereto and generating a signal representative ofmeasured tissue impedance; comparing the measured tissue impedance witha predetermined maximum impedance value; transmitting to theelectrosurgical generator unit a signal to cease or limit further energydelivery if the measured tissue impedance exceeds the predeterminedmaximum impedance value; passing a fluid through the lumen at a desiredflow rate to regulate the temperature of the energy deliveringelectrode; and regulating the flow rate to maintain the tissue impedanceat or below the predetermined maximum impedance value.
 2. The method ofclaim 1 wherein the flow rate is in the range of 1 to 50 ml/minute. 3.The method of claim 1 further including the step of increasing the flowrate when the measured tissue impedance value exceeds the predeterminedmaximum impedance value.
 4. A system for controlling the temperature ofan energy delivering, cauterizing electrode, comprising:an elongateelectrosurgical probe member having a central lumen disposed therein toenable fluid to be conveyed through the probe member for discharge at adistal portion of the probe member, the probe member having at least oneenergy delivering electrode disposed at a distal portion of the probemember; an electrosurgical generator unit in electrical communicationwith the probe member for supplying electrosurgical energy to theelectrode for delivery to tissue adjacent to the electrode; a fluidsupply source in communication with the lumen; impedance measuring meansfor measuring tissue impedance based on the energy applied thereto;impedance comparing means for comparing the measured tissue impedance toa predetermined maximum impedance value, the impedance comparing meansgenerating a disabling signal if the measured impedance value exceedsthe predetermined maximum impedance value; means for communicating thedisabling signal to the electrosurgical generator unit to cease furtherdelivery of energy from the generator unit to the probe member; andfluid control means for regulating the rate of flow of fluid through thelumen to maintain the measured tissue impedance at or below apredetermined maximum impedance value.